This invention relates to coffee bean roasting systems and more specifically to a method and apparatus for increasing the energy efficiency and utilization of roasting systems while improving the quality of the roasted coffee beans.
There are two primary methods for roasting coffee beans. Drum roasting uses a heating technique similar to common clothes dryers. Green coffee beans are placed in a round drum. Heating elements heat both the drum and the air inside the drum. As the drum rotates, the coffee beans are circulated inside the rotating drum. The heat from the inside walls of the drum is transferred to the coffee beans. As the coffee beans continue to roll inside the drum, the coffee beans are heated and scorched, changing from a green state to a roasted condition. To generate darker roasts, the coffee beans are heated in the drum at a higher temperature.
A fluid bed roaster blows air up from the bottom end of a roasting chamber. The air raises the green coffee beans up on a bed of hot air causing the beans to circulate inside the chamber. U.S. Pat. No. 3,964,175 to Sivetz shows a fluid bed coffee roasting system. In Sivetz, air is heated to a selected temperature and the heated air roasting the coffee beans primarily by convection. The beans are roasted secondarily by conduction of heat from bean to bean and from conduction of heat from the inside walls of the roasting chamber to the coffee beans.
Coffee roasting systems generate a substantial amount of smoke and chaff when bean temperatures go over 300 degrees. External ventilation systems are needed to filter the smoke and other pollutants away from the room where the coffee roasting is taking place. After-burners are used to burn-off some of the smoke and pollutants before venting coffee bean exhaust to the outside environment. After-burners significantly increase the amount of energy used during each roasting session. After-burners are also not very effective in removing tar and other pollutants from the coffee bean exhaust. Thus, current roasting systems must be operated in industrial locations where objectionable exhaust fumes cannot be inhaled by retail coffee consumers.
Roasting machines must produce consistent bean roasts for a wide variety of desired bean flavors. Special skill is required to reproduce consistent coffee bean roasts with current coffee roasting machines. A roast-master must visually inspect each batch of roasted coffee beans for a desired bean darkness. If lighting in the roasting room changes, the perceived color of the roasted coffee beans changes. If not circulated evenly inside the roasting chamber, coffee beans will not roast evenly. Thus, even a skilled roast-master has difficulty reproducing consistent coffee roasts.
U.S. Pat. No. 3,964,175 to Sivetz shows in FIGS. 3 and 8, the circulation pattern for coffee beans in two different sized roasting chambers. A majority of the coffee beans follow a circulation pattern that first travels up the entire vertical length of a front wall then down an inclined back wall. A smaller number of coffee beans are suspended in the center of the chamber making minimal contact with the front and back walls. The coffee beans consistently riding against the inside walls of the roasting chamber have a higher likelihood of burning or becoming darker than the coffee beans that spend a substantial portion of time circulating in the center of the chamber. Thus, the coffee beans will not have a consistent roast condition.
The water content of green coffee beans can differ. Different batches of coffee beans may, therefore, require different amounts of heat to reach the same temperature. Sivetz uses a thermometer to measure the air temperature inside the roasting chamber, but does not measure the actual temperature of the coffee beans. Thus, two different batches of coffee beans, roasted at the same air temperature for the same amount of time, might produce two substantially different roasting results.
Accordingly, a need remains for a low pollutant and energy efficient roasting system that produces more consistent coffee bean roasts.